Browsing by Subject "Stress (Physiology)"

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The effects of stress on different stages of memory
(2004) Beckner, Victoria Lemle, 1966-; Tucker, David M., 1953-; Markman, Arthur B.
Research suggests that memory is influenced by stress and the associated rise of glucocorticoids, such as cortisol. While human studies have generally found a negative effect of stress and elevated cortisol on memory, animal studies have demonstrated a dose-dependent facilitative effect. These discrepant findings may be a result of methodological limitations in the human literature, which often confound the different stages of memory by elevating cortisol levels prior to encoding, consolidation and retrieval. The purpose of the current study was to parse the effects of an acute psychosocial stressor on these separate memory processes by varying the timing of the stressor. Based on recent evidence, we predicted that stress would enhance encoding and consolidation, but impair retrieval. 208 college students (63 male, 138 female, mean age = 18.9) were randomly assigned to a no-stress control group (n = 51) or one of three groups stressed at different time points: prior to stimulus presentation (encoding/ consolidation, n = 51), immediately after stimuli presentation (consolidation, n = 56), or just before memory testing 48 hours later (retrieval, n = 50). Salivary cortisol was measured at baseline and 20 minutes after the stressor. Both verbal and visual memory was measured at the 48-hr delay using a film stimulus developed by the investigator and with the WMS-III narrative. Results demonstrated that the group stressed prior to consolidation significantly outperformed controls on the film recognition at delay for verbal and total scores. This effect may have been related to cortisol response, as this was the only stress group to exhibit a significant increase in cortisol (40%) following the stressor. No significant differences in memory were found between the other stress conditions and controls. Within-group correlations between change in cortisol and memory were not significant, but exploratory analyses revealed a small but significant positive correlation for cortisol and verbal scores on the film recognition test across all groups (rxy = .18). Results support the hypothesis that stress enhances consolidation of new information, and provides the first evidence of this for verbal memory. Findings did not support a detrimental effect of stress on retrieval.
Network mechanisms underlying susceptibility to helplessness and response to the antidepressant fluoxetine
(2010-05) Padilla, Eimeira; González-Lima, Francisco, 1955-; Delville, Yvon; Domjan, Michael P.; Dominguez, Juan M.; Beevers, Christopher G.
Depression and post-traumatic stress disorder are common psychiatric comorbidities related to stress. These conditions are frequently treated with antidepressants such as selective serotonin reuptake inhibitors (SSRI’s). However, there are individual differences in susceptibility to stress-induced psychopathologies and response to antidepressants. Therefore, there is a need to identify biologic factors that predict vulnerability to stress and response to treatment. Furthermore, few studies have examined the neural correlates of antidepressant treatment response in a stress-susceptible animal model. This dissertation had three specific aims: 1) to characterize behavioral predictors of stress vulnerability by studying three dimensions of temperament (reward dependence, novelty-specific activity and harm avoidance) before stress exposure using a stress-susceptible rat strain, 2) to identify the neural network effects of response and non-response to SSRI treatment using a stress-susceptible animal model, and 3) to determine the neurophysiologic correlates of helplessness susceptibility. This was examined via measurement of regional brain metabolic capacity and functional connectivity within relevant neural circuits, and measurements of corticosterone and heart rate. These effects were studied in rats that underwent inescapable shock exposure followed by escape testing. Holtzman rats showed greater predisposition to helpless behavior following inescapable shock compared to Sprague Dawley and Long-Evans strains. Also, increased activity in a novel environment and low heart rate appeared to be markers of helplessness susceptibility in Holtzman rats. Limbic-cortical network effects were identified that distinguished between responders and non-responders to antidepressant treatment in the Holtzman strain. Finally, hypermetabolism of the lateral habenula and a less interactive prefrontal-limbic cortex were identified in subjects with higher susceptibility towards helplessness within the Holtzman strain. Similar findings have been reported with other depression animal models and human neuroimaging studies. These findings support that the helpless dimension of mood disorders can be accurately modeled with the Holtzman rat strain and confirm that the lateral habenula and prefrontal cortex are key regions mediating the helpless phenotype and response to SSRI treatment.
Overgeneral cognitive style : the impact on physical and emotional adjustment to life stress
(2002-08) Gibbs, Bryce Neil; Rude, Stephanie Sandra
Research has found that individuals who are depressed and have experienced past traumas tend to report vague or overly general autobiographical memories (AM) and evidence prolonged latencies to retrieve specific AM’s (Kuyken & Brewin, 1995; Kuyken and Dagleish,1995). Additionally, other researchers have demonstrated that individuals who possess AM deficits have associated difficulties with social problem solving (SPS) (Goddard, Dritschel, and Burton, 1996) and display overgenerality in their imaginings of the future, which has been linked to the hopelessness that often accompanies depression (Williams et al., 1996). Finally, in terms of trauma, researchers have speculated that deficits in AM prevent individuals who have experienced trauma from restructuring their traumatic schemata thereby engendering psychopathology (Harvey, Bryant, and Dang, 1998). Based on the aforementioned research, this dissertation investigated whether AM deficits act as “diatheses” that predispose individuals to psychopathology, especially those with histories of trauma and who are currently experiencing life stress (Abramson, Alloy, and Metalsky, 1988). A starting point for the study was the notion that overgeneral (OG) memory may exist as a broad means of avoiding painful affects associated with traumatic memories. To this end, it was hypothesized that OG memory as assessed by established assessments of this construct would be associated with OG memory as assessed by a narrative measure of overgenerality. Second, due to the associations between AM deficits and related cognitive abilities (i.e. SPS and OG imaginings of the future), it was hypothesized that individuals with AM deficits would experience greater physical and emotional distress over the course of the semester than those without this vulnerability. Third, in agreement with established “diathesis-stress” models, it was hypothesized that AM deficits would interact with life stress over the course of the semester and lead to greater levels of physical and emotional distress than in “stressed” participants without the diathesis. Finally, based on the theory that AM deficits hinder individuals from restructuring traumatic schemata, it was hypothesized that AM deficits would mediate the relationship between past trauma and current physical and emotional distress. Results supported the hypothesis that overgeneral memory and latencies to provide specific memories would interact with life stress to predict emotional distress over the course of a semester. However, overgeneral memory and latencies to provide specific memories did not independently predict physical or emotional distress over the course of the semester and were not found to mediate the relationship between past trauma and current distress.